The invention relates to an absorbent structure intended for use in an absorbent article such as a sanitary napkin, a diaper, or an incontinence guard, whereby the absorbent structure comprises two different material types which are in direct or indirect contact, so that liquid may be transferred between the material types.
When manufacturing an absorbent article of the above-mentioned kind, it is often desirable to be able to provide the article with a three-dimensional shape which is adapted to the anatomy of the user of the article. By designing an absorbent article so that it follows and conforms to the body shape of the user, a number of advantages are namely achieved, such as increased comfort for the user, increased leakage-security and improved discretion, i.e. the article may more easily be concealed underneath the clothing of the user.
An obvious difficulty in connection with the shaping of an absorbent article is, however, that the shape of the article changes during use. The deformation is particularly obvious after wetting of the article. Cellulose fluff pulp is an absorbent material which is often used in absorbent articles. Cellulose fluff pulp is a readily available and comparatively cheap absorbent material which, for example by means of air-laying, may be relatively easily utilized in order to give an absorbent article a desired shape. A considerable disadvantage with cellulose fluff pulp is, however, that the material collapses when it is wetted and loses its original shape. An absorbent article with an absorbent structure manufactured from cellulose fluff pulp will consequently only maintain an original, three-dimensional shape in an initial stage, before the article has absorbed body fluid.
Another disadvantage with absorbent structures which consist of cellulose fluff pulp is that they have a reduced volume after wetting. This implies that the fibre structure within the wet region has thinner capillaries than surrounding dry fibre material. Thus, liquid distribution in the absorbent structure is counteracted so that the liquid for the most part remains in the initially wetted region of the structure. This region is therefore rapidly saturated with liquid and is thereafter unable to absorb additional liquid which is emitted to the absorbent structure. As a consequence, there is a large risk that the liquid, instead of penetrating into the absorbent structure, flows out over the surface on the absorbent article and causes leakage.
The problem with insufficient shape permanence of absorbent articles is particularly obvious in connection with sanitary napkins and other absorbent articles which have a proportionately small size and which are intended to be worn inside a pair of ordinary panties. Since such articles of necessity are fairly narrow, leakage of body fluid out past the longitudinal side edges of the article is not an untypical problem. Such leakage is of course highly undesired, since it entails the risk of soiling the clothing of the user. Due to the rather short extension of the article in the longitudinal direction, it is furthermore not unusual that liquid also leaks out forwards and backwards, past the end edges of the article. Rearwards-leakage is a particular problem which, as a rule, arises when the user is lying down, for example during the night.
One way of reducing the risk of edge leakage caused by deformation of the article during use is to provide the article with a pre-formed hump which, during use, is intended to be in contact with the genitals of the user. In this way, excreted body fluid may be caught as soon as it exits the body of the user, and immediately absorbed into the article without flowing out over the surface thereof.
Previously known absorbent articles provided with a liquid-receiving hump are, however, afflicted with a number of disadvantages.
A common way of creating a hump has been to simply build it up by means of arranging a larger quantity of absorbent material within the region of the hump. Since the most commonly used absorbent material is cellulose fluff pulp, such a hump collapses and loses its shape when it is wetted. In order to obtain a hump which is also sufficiently large in a wet state, a hump consisting of cellulose fluff pulp has to comprise so much absorbent material that is becomes far too high, hard and uncomfortable to wear in a dry state.
In order to solve the problem with large, hard and uncomfortable humps, it has been suggested in EP 0 339 041 to provide the liquid-impervious surf ace of the article with transverse elastic members. Such elastic members impart a certain resiliency to the article in case it is subjected to flattening. However, t he elastic members do not to any great extent prevent the hump from being compressed and from changing shape during use.
In another publication, EP 0 419 434, it has been suggested to create a soft hump on an absorbent article by means of locking the side edges of the article at a mutual distance which is smaller than the planar distance between the side edges. Neither does this known article, however, retain its shape during use.
In EP 0 335 252 and EP 0 335 253 it has been suggested to provide an absorbent article with a deformation element. The deformation element is influenced by the transverse compressive forces between the thighs of a user. The purpose of the deformation element is that, during use, it creates a bulge in a portion of the article in a direction towards the body of the user. However, it is impossible to completely control, or predict the shape the article will adopt for each individual user. Furthermore, it is not possible to ensure contact between the body of the user and the surface of the article, since the degree of bulging is completely determined by how much the article is compressed in the transverse direction.
Accordingly, there remains a need for a leakage-proof absorbent article which has a predictable shape, both before and during use, and which maintains its shape independently of the wetting the article is subjected to.
An article designed according to the invention and of the type mentioned in the introduction, is primarily characterized in that the first material type is constituted by material which swells when absorbing body fluid, and the second material type is constituted by material which collapses when absorbing body fluid, whereby the volume increase in the first material type is essentially as large as the volume reduction in the second material type when the absorbent structure is saturated with liquid, whereby the absorbent structure has substantially the same volume both in both a wet and a dry state.
By ensuring that the volume of the absorbent structure is practically constant, independently of whether the structure is dry or wet, according to the invention it is possible to provide absorbent articles with very good shape permanence.